1. Field of the Invention
The present invention relates to novel 2-pyrazolin-5-ones and a novel process for production thereof as well as novel hydrazone derivatives which are intermediates for synthesis of the aforesaid 2-pyrazolin-5-ones and a process for production thereof.
2. Brief Description of the Prior Art
2-Pyrazolin-5-ones are useful as intermediate raw materials for drugs represented by antipyrine and various investigations have been hitherto made also on a process for production thereof.
In recent years, it has become clear that 2-pyrazolin-5-ones are also useful as intermediate raw materials for herbicides (U.S. Pat. No. 4,063,925, U.S. Pat. No. 4,230,481, U.S. Pat. No. 4,406,688 and U.S. Pat. No. 4,557,753) which are a series of compounds that are expected to expand their applicable range more in the future.
As a process for production of such 2-pyrazolin-5-ones, for example, the following reaction is known: ##STR3## wherein R.sup.7 represents, e.g., a lower alkyl group; R.sup.8 represents, e.g., a hydrogen atom or a lower alkyl group; and R represents, e.g., a hydrogen atom, a methyl group or a phenyl group.
This reaction is a process for obtaining the desired 2-pyrazolin-5-ones from mono-substituted hydrazines and .beta.-keto esters at one step, which generally gives a high yield and is an excellent process.
However, a problem of this process lies in that there is a restriction in access to the raw .beta.-keto esters and monosubstituted hydrazines.
For example, 1-substituted-2-pyrazolin-5-ones which are most typical 2-pyrazolin-5-ones wherein R.sup.7 and R.sup.8 represent hydrogen atoms are not prepared by this process because formylacetic acid ester used as a raw material thereof is unstable.
In addition, mono-substituted hydrazines shown by RNHNH.sub.2 are not easily accessible, except for some of hydrazines in which R is a phenyl ring, an aromatic hetero ring and a methyl group; after all, 2-pyrazolin-5-ones which can be produced at low costs are restricted also in this aspect.
A reaction shown by: ##STR4## is also known.
According to this reaction, however, compounds which are easily prepared are restricted due to difficult accessibility to the mono-substituted hydrazines as in the case of (1), acetylenecarboxylic acid esters as another raw materials are not necessarily readily accessible in an inexpensive way, by-products are generally easily produced and as a result, the yield is not always high and purification is not easy. After all, it should be said that industrial practicability is poor.
For the reasons described above, notwithstanding that investigations have been made on the process for production of 2-pyrazolin-5-ones over long years and, for example, many 3-methyl-2-pyrazolin-5-ones have been synthesized, 3,4-unsubstituted 2-pyrazolin-5-ones are a series of novel compounds that have not been synthesized yet except for several compounds.
These exceptional several compounds were synthesized by the process shown below: ##STR5## (Dorn. Hetall, J. Prakt. Chem., 115 (1971)).
According to this process, compounds wherein R is methyl and benzyl can be prepared. However, this process is not preferred because the N atom on the pyrazoline ring should be once protected by an acetyl group, alkylation also occurs on the oxygen atom and therefore the reaction becomes complicated and, removal of the by-products and acetic acid by-products is also troublesome, etc.
Further, the synthesis of 1-(p-chlorobenzyl)-2-pyrazoline is reported in U.S. Pat. No. 3,952,008. The synthesis is based on the process (2) described above and not preferred for the reasons described above.
Furthermore, the process shown in (4) has been developed in recent years. ##STR6## This process is superior to the process (3) but inferior to the process of the present invention in view of operations and costs because methylhydrazine is much more expensive than the unsubstituted hydrazines used in the present invention, ethoxymethylenemalonic acid diester is also expensive, an isomer: ##STR7## is by-produced, etc.
In addition, the scope of the substituent R capable of easily producing 2-pyrazolin-5-ones is narrow due to difficult accessibility to the mono-substituted hydrazines described in (1) so that this process is far inferior to the process of the present invention.